The disclosures herein relate generally to implantable prostheses for replacing human skeletal joints, and more particularly to a universal distal broach and implant stem trial for sizing left and right femurs.
Implantable orthopedic prostheses, in one form, comprise manufactured replacements for the ends and articulating surfaces of the bones of the skeleton. Such prostheses are implanted to repair or reconstruct all or part of an articulating skeletal joint that is functioning abnormally due to disease, trauma, or congenital defect. Among the various articulating skeletal joints of the human body that are eligible to be fitted with implantable orthopedic prostheses, the hip joint is one of the joints most often treated with such prostheses. The hip joint is a major weight bearing joint and degenerates relatively quickly in case of abnormality. Also, the hip joint plays a critical role in ambulation and quality of life, resulting in great demand for surgical correction of abnormalities.
The human hip joint involves two bones: the femur and the pelvis, each having a smooth articulation surface arranged for articulation against an adjacent articulation surface of the other bone. The femur includes at its proximal extremity a head having a convex, generally spherically contoured articulation surface. The pelvis, in pertinent part, includes an acetabulum having a concave, generally spherically contoured articulation surface. The mutually engaging articulation surfaces of the femur and the pelvis together form, functionally, a ball-and-socket joint.
As used herein, the words proximal and distal are terms of reference that indicate a particular portion of a prosthesis component according to the relative disposition of the portion when the component is implanted. "Proximal" indicates that portion of a component nearest the torso, whereas, "distal" indicates that portion of the component farthest from the torso. Directional terms of reference used herein include superior, inferior, anterior, posterior, medial and lateral, which are used according to their commonly understood anatomical meanings. More particularly, with regard to a person in a standing position, superior means upward, inferior means downward, anterior means forward, posterior means rearward, medial means inwardly from the side toward the center of the body, and lateral means outwardly from the center of the body toward the side.
One or both of the articulation surfaces of the hip joint may fail to act properly, requiring the defective natural articulation surface to be replaced with a prosthetic articulation surface provided by an implantable prosthesis. To fit defects of varying scope, while allowing healthy portions of the hip joint to be conserved, a range of types of orthopedic implants is available. The range extends from total hip prosthesis systems for replacing the articulation surfaces of both the femur and the pelvis, to less comprehensive systems for replacing only the femoral articulation surface. Commonly employed orthopedic hip prostheses include components that fall within one of three principle categories: femoral stems, femoral heads and acetabular cups. A so-called "total" hip prosthesis includes components from each of these categories. The femoral stem replaces the proximal end of the femur and includes a distal stem received within the medullary canal at the proximal end of the femur. The femoral head replaces the natural head and articulating surface of the femur. The acetabular cup replaces the natural socket and articulating surface of the acetabulum of the pelvis. In some designs, the stem and head are an integral, unitary component, but more often the stem and head are separate modular components designed to be assembled to suit the anatomical needs of the patient. A so-called "bipolar" hip prosthesis includes only femoral stem and head components. The femoral part of the hip joint is replaced with a femoral stem supporting an artificial femoral head. The latter includes an inner head, fixed to the femoral stem, that articulates within an outer head. The outer head articulates directly against the natural acetabulum. Similarly, a so-called "unipolar" hip prosthesis also includes only femoral stem and head components. The femoral part of the hip joint is replaced with a femoral stem supporting an artificial femoral head. The femoral head articulates directly against the natural acetabulum while remaining fixed relative to the femoral stem.
The acetabular cup component of a total hip prosthesis is configured to be received and fixed within the acetabulum of a pelvis. The pelvis is prepared to receive the acetabular cup by reaming a concavity in the acetabular bone. The acetabular cup component typically has an outer surface conforming to the concavity reamed in the acetabular bone of the pelvis, and an inner bearing cavity for receiving the head of the femoral component. The head articulates in the bearing cavity as a ball-and-socket joint to restore motion to a defective hip joint. One common type of acetabular cup involves an acetabular shell made of a bio-compatible metal such as titanium or a titanium alloy, and a bearing insert made of a bio-compatible polymer such as ultra-high molecular weight polyethylene. The acetabular shell is shaped generally as a hemispherical cup having a dome, or apex, at a proximal end and an annular rim at a distal end. The acetabular shell includes a concave distal surface between the apex and annular rim that defines a shell cavity having an opening at the rim of the cup for receiving the bearing insert. The bearing insert has a generally convex proximal surface for receipt and fixation within the acetabular shell in generally congruent engagement with the concave distal surface of the shell wall. The bearing insert also has a bearing cavity that opens distally for receiving the head of the femoral component. The bearing cavity is defined by a generally spherical concave bearing surface having a radius similar to that of the femoral head component. The concave bearing surface articulates against the surface of the spherical femoral head component. The acetabular shell can be affixed to the acetabular bone by bone screws or bone cement. If bone screws are elected, the screws are driven into the bone through the screw holes before the bearing insert is placed into the shell. The shell also can be affixed by a combination of a bone screws and bone cement.
The femoral stem component typically is constructed as an integral unit having a distal stem, a proximal body and neck. The distal stem is relatively elongated and generally cylindrical or slightly conical and sized to fit within the relatively narrow intra medullary canal near the proximal end of the femur. The proximal body extends superiorly from the proximal end of the distal stem and is sized to fit within and substantially fill the expanded intramedullary canal at the proximal end of the femur. The neck extends superiorly and medially from the proximal body at an angle of about 45 .degree.. The orientation of the neck is designed to replicate the natural orientation of the natural neck of the femur. The proximal end of the neck typically is configured as a male conical taper, or Morse taper, for frictionally interlocking with a mating female conical taper formed in the prosthetic femoral head. The femoral stem can be affixed to the femoral bone surrounding the intramedullary canal by bone cement and rely on bone growth adjacent the implant to secure the implant in place.
The femoral head component is configured substantially as a polished sphere having a blind hole therein shaped as a female conical taper, or Morse taper, for frictionally interlocking with the male conical taper of the neck. The femoral head can also include an integral boss surrounding the blind hole and extending from the head, permitting the offset of the head relative to the femoral stem to be increased.
To implant the femoral stem component, a typical surgical procedure involves resecting the natural neck and head of the proximal femur by performing an osteotomy along a plane oriented substantially perpendicular to the axis of the natural neck. The natural head and neck is removed, exposing the proximal medullary canal of the femur. Specially configured instruments are used to remove cancellous bone from the proximal intramedullary canal and shape a cavity within the cancellous bone that is closely complementary to the external shape of the femoral component. If permitted by the patient's anatomy, it is desirable to enlarge the cavity to the inner wall of the cortical bone and use a prosthesis large enough to engage the cortical bone. This provides secure fixation of and support for the femoral stem.
The cavity that is to be formed in the proximal intramedullary canal is generally elongated and cylindrical or slightly conical at the distal end, and generally oval or trapezoidal in cross-section and tapered longitudinally at the proximal end. To form such a cavity, it is common to employ a rotary reamer to ream the distal portion of the cavity. The rotary reamer is then withdrawn and a broach, shaped like the proximal portion of the femoral component, is repeatedly driven into the proximal intramedullary canal. The broach usually has a stem extension that extends into the previously reamed distal portion of the cavity to serve as a pilot to guide the broach, the proximal portion of which is fitted with cutting surfaces. Often, the pilot stem pistoning in the reamed distal portion of the cavity does not provide enough directional stability to assure that the broached proximal portion of the cavity is well aligned with the reamed distal portion of the canal. The result is a cavity that may not conform as closely to the external shape of the femoral implant as desired.
Prior to implanting the femoral stem, it is useful for the surgeon to be able to confirm that the bone cavity has been reamed to the proper depth. The provides assurance that the center of rotation of the femoral head will be properly located to restore the hip joint to an anatomically correct condition. One method of confirmation is to withdraw the broach and insert a trial femoral stem component into the reamed and broached cavity, and to perform a trial reduction of a joint using a trial femoral head on the trial stem. If the trial reduction indicates that further broaching or reaming of the cavity is required, the trial stem must be withdrawn, the broach must be reinserted, and the procedure must be repeated. To reduce the complexity of the procedure, it is also known to use a broach having means to which a trial femoral head can be attached, thereby permitting the trial reduction to be performed while leaving the broach in place to serve as the trial stem.
In U.S. Pat. No. 5,607,431, a surgical instrument system for preparing the medullary canal of the femur for implanting a prosthetic femoral component includes a template to be used in determining osteotomy position from an x-ray. A gauge is provided to locate and mark this position on the anterior femur. A distal reamer having an elongated drive shaft is used to form the canal to receive the distal stem of the femoral component. A metaphyseal template is used to determine the proper anteversion/retroversion and a chisel is used to cut the lateral area of the femur, both of which are guided by the elongated reamer shaft. A proximal broach also guided by the reamer shaft is used to shape the proximal medullary canal.
Therefore, what is needed is a universal distal broach and implant stem trial which can be used in either the left or right femur, and therefore reduce the instrumentation inventory.